1. Field of the Invention
The present invention relates to a fastening torque control tool of a fastening device for making constant the fastening torque by a fastening material, that is the joint strength, in fastening by use of the fastening material such as a bolt or a screw.
2. Description of the Related Art
As illustrated in FIG. 5 and FIG. 6, for example, in a case 3 consisting of a top box 1 and a bottom box 2 coming into contact with the top box 1, the top box 1 is connected to the bottom box 2 by a plurality of bolts 4 which act as fastening devices and which extend through the top box 1, in the conventional technique.
In these drawings, a concave portion 5 is formed on the top surface of the top box 1, and a through hole 6 of a smaller diameter than that of the concave portion 5 is formed continued from the concave portion 5. A tapped hole 7 positioned along the same axis as that of the through hole 6 is formed on the inside of the bottom box 2. After bringing the bottom box 2 into contact with the top box 1, the bolt 4 as the fastening device is inserted into the concave portion 5 and the through hole 6. The bolt 4 is screwed down into the tapped hole 7 of the bottom box 2, thereby connecting both boxes 1 and 2.
The bolt 4, that is, for example, a hexagon socket head cap screw, is screwed by a hexagonal wrench 8 as a fastening instrument.
This fastening method requires management of the fastening torque, in some cases, in order to prevent the occurrence of disadvantages such as looseness after fastening. Management of the fastening torque is also required to make the fastening forces of a plurality of fastening devices uniform.
The above-mentioned torque control is performed by using a tool provided with a torque control function, such as a torque wrench, in the manufacturing line or the assembly line of a factory.
Under present conditions, however, at the assembly time or maintenance time in the site, the above-mentioned tool provided with the torque control function is rarely used. The torque control cannot help relying on the sense of a worker, and the constant fastening torque cannot be always obtained.
Even if fastening can occur with the tool provided with the torque control function in the factory, there is a possibility that the fastening will be performed by a torque other than the established torque. Moreover, once it is fastened, it is impossible to confirm the fastening torque.